Optically pumped laser systems with high power conversion efficiency will enable them to be used in applications that require compactness or portability. The power conversion efficiency includes the efficiencies of the optical pump laser as well as of the optically pumped laser. The need for improved pump light utilization of optically pumped lasers has been known for many years, with the best power conversion efficiency achieved (for semiconductor lasers emitting at 3-5 micron wavelengths) being only 0.08 per output facet at a temperature of 200K. The present disclosure aims to improve that power conversion efficiency while also operating at room temperature.
A substantial amount of related, but different, prior art exists for optically pumped semiconductor lasers. However, the prior art has not used an integrated optical pump with a longitudinal-cavity optically pumped laser and especially with an optically pumped external-cavity laser. The best prior attempt at improving the efficiency of optically coupling the pump light to an optically pumped laser is described in Applied Physics Letters, v. 75, n. 19, pp. 2876-2878 (1999). This prior work employs a separate (not integrated) optical pump laser with the pump light vertically incident on the optically pumped laser. A vertical optical cavity is formed in this prior art to achieve multiple passes of the pump light. In contrast, for the present invention the pump light co-propagates in the longitudinal direction with the light generated by the optically pumped laser. The present invention also places the gain medium of the optically pumped laser within the longitudinal optical cavity for the pump laser.
A vertical-cavity semiconductor laser with an integrated optical pump has been described by V. Jayaraman in U.S. Pat. Nos. 5,513,204 and 5,754,578 and in Electronics Letters, v. 34, n. 14, pp. 1405-1407, 1998. However, these prior lasers are vertical-cavity devices wherein light from the pump laser is coupled into the optically pumped laser through the high-reflection mirror of the pump laser rather than by having the transverse optical-field distribution of the pump laser at least partially overlap the gain region of the optically pumped laser, as disclosed presently. The pump laser and the optically pumped laser described by V. Jayaraman are arranged end to end. In contrast, the pump laser portion and the optically pumped gain element portion of the laser disclosed herein are arranged side to side, sharing the same end facets of the substrate material and having their transverse fields at least partially overlap.